Get a star. This will allow you to be invincible and go through stuff. There's a lot of stuff you can go through. For example, in the Kalamari Desert in the Mushroom Cup, you can go on the railroad. Then, drive towards the train and activate the star. You'll go through the train with no problem and be able to see its insides.
You can also go through the egg in Yoshi Valley in the Special Cup while invincible. Not so much to look at, though.